Deciding the number of bulls needed

Admitted or not, in the cow-calf business, bulls are often viewed as nothing more than necessary overhead, like fuel or feed — interchangeable commodity products, one basically the same as another. Plenty of folks base their bull-buying decisions more on price than genetic merit. Ironically, these folks may have higher overall bull costs than peers who pay the highest average cost for bulls.

“It's been our experience we (industry) run far too many bulls simply because we're scared we won't get the cows covered,” says Bob Prosser, Bar T Bar Ranch, Winslow, AZ. "Every rancher has been in a situation where cows didn't get bred. But when you look at the numbers, the bull-to-cow ratio may not be the most cost-effective insurance policy."

Understand, Prosser and his family run cows in high, sprawling, arid and rugged country. In fact, they developed their seedstock herd to provide genetics suited to their ongoing commercial operation.

Prosser explains, "One of the primary factors affecting bull cost per weaned calf is the stocking rate of bulls to cows. Common sense tells us two major factors affect bull breeding needs: the number of available waters and the percentage of cows bulling on any given day."

Depending on where you live, historic bull-stocking rates can run from one bull to 10 cows up to one bull to 30 or more cows. It depends on the country, the age and ability of the bulls, but not necessarily logic.

In fact, leading animal scientists, like Peter Chenoweth at Kansas State University, have pointed to research that indicates traditional bull-to-female ratios (BFR) are less important than bulls' fertility, libido and mating ability. In 2000, he reported that in natural breeding situations — multi-sire or single-sire — BFR underestimates the reproductive capability of competent bulls.

Bull-to-female ratios The way Prosser sees it, "A cow's reproductive cycle is 21 days. Few if any operations have all their cows bulling in that 21 day window." As a conservative rule of thumb, figure that, on average, three-quarters of the cows will come into heat in a 21-day cycle. Divide that number (cow herd × 75%) by the number of days the majority of them calve and it's a good indicator of the number of cows cycling any given day. That's also a good indication of how many bulls you actually need to breed the cows.

For simplicity, let's say you have 100 cows and most of the calves are born in a 75-day window. Using Prosser's 75% guide, you'd figure 75 of those cows would cycle on average during any 21-day period. A 75-day primary calving season would mean that, on average, there was only one cow cycling on any given day of that 75-day breeding season.

So, if your stocking rate is one bull to 30 cows (on 100 cows, as in the example), you basically have a little better than three bulls to cover a cow when she's cycling. If you run a bull to 25 cows, you've got four bulls to cover each cycling female, and so on.

"We all know cows don't cycle on the average, and numerous cows will be in heat on a given day in the middle of the breeding season. But you can see that even a stocking rate of 1 to 30 will cover three times the average number of bulling cows (see chart below)," Prosser explains.

"Certainly, range with numerous waters or topography issues impact bulls' effectiveness in getting the cows covered," he adds. "But we need to ask ourselves if our bull-stocking rates are based on realistic needs, or on a time when many bulls in the industry weren't fertility tested and pastures weren't cross-fenced?"

Obviously, different geography and goals have different demands. And, exploiting this opportunity requires having bulls with the history, predictability and testing that suggest they can go out and breed rather than loaf.

"Getting cows bred is the issue, and we all need to be able to sleep at night," Prosser says. "But buying a bunch of cheap bulls with little information to get the cows covered may not be the wisest use of resources."